The interaction of vaccinia virus-coded proteins which bind to viral nucleic acid during the infectious cycle and in mature virus particles will be purified and studied with regard to their effects on the structure of DNA and the process of viral DNA replication, transcription, and packaging. One of these proteins is an enzyme capable of relaxing supercoiled DNA. This relaxing enzyme will be studied both in terms of its reaction mechanism and role in the infectious cycle. Studies will be continued utilizing the recently developed methods for nuclear transplantation which involve the use of cytochalasin B for enucleation of cells and the subsequent fusion of karyoplasts with cytoplasts utilizing Sendai virus. Studies will also be conducted on the ability of karyoplasts, nuclei surrounded by a small amount of cytoplasm and the plasma membrane, to regenerate new cytoplasm. These studies are expected to shed light on the ability of cytoplasm to modify the expression of nuclear genes. BIBLIOGRAPHIC REFERENCES: Lucas, Joseph J., Elizabeth Szekely, and Joseph R. Kates, "The Regeneration and Division of Mouse L-Cell Karyoplasts," Cell, 7,000, January 1976. Lucas, Joseph J. and Joseph R. Kates, "The Construction of Viable Nuclear-Cytoplasmic Hybrid Cells by Nuclear Transplantation," Cell, 7, 397-405, March 1976.